Brood X Cicadas – They’ll Be Back

By Kristin Winters, HLT Land Steward

Anyone who visited HLT’s Quakertown Preserve earlier this summer may have wondered why an unusually loud burglar alarm was sounding in the woods. A quick walk along the trail would have revealed the source. It was no burglar – just a massive crowd of noisy, busy cicadas!

While some areas of Hunterdon County were quiet, others heralded the arrival of the regionally famous Brood X (Roman numeral 10) cicadas. Brood X is one of the largest groups of periodical cicadas in the world. They emerge in 15 states, with concentrations in the Mid-Atlantic region, Indiana, Ohio and Tennessee.

While there are more than 3,000 species of cicadas on the planet, periodical cicadas reside in the eastern U.S.; the broods emerge in different years, and their ranges fit together across the region like a jigsaw puzzle. Annual broods ensure that there are always cicadas around, typically in the latter half of the summer. Our local annual cicadas are Neotibicen canicularis.

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Periodical Cicadas	Annual Cicadas
Emerge after 13 to 17 years	Emerge after two to five years
Black and reddish-orange in color	Black, green and white in color
Larger in size	Smaller in size

Like annual cicadas, periodicals have two large eyes and three small ones in between, but their large eyes are a distinctive reddish-orange color. While underground, periodical cicadas feed on tree root sap, and develop from nymph to adult until they emerge in May/ June at a rate of up to 1.4 million insects per acre!

Why so many at once? It is thought that periodical cicadas have evolved their precise schedule owing to a survival strategy called “predator satiation”; there are so many insects at one time that predators can’t eat them all. Scientists don’t entirely understand how cicadas time their simultaneous emergence, but it may be related to changes in the tree sap or weather. Immediately after emerging, cicadas shed their nymphal exoskeletons, climb on a vertical surface, and allow their shells to harden for a few days, changing from white to darker colors. The males emerge first, and many do get eaten, but enormous numbers (especially females) remain to produce the next generation.

The females lay hundreds of eggs in the branch tips of deciduous trees; the branch tips die, turn orange, and droop down (called “flagging”). Regions where periodical cicadas have laid eggs can be identified by the orange-polka-dotted trees! While young trees may be damaged by flagging (the trees can be protected with nets), more mature trees are not usually harmed. Humans and wildlife don’t have to worry either; our local cicadas don’t sting, bite, or carry diseases, and don’t enter buildings unless they accidentally hitch a ride on a person or packages.

The cicadas are, however, noisy! To attract mates, males use a drum-like apparatus called a tymbal organ to create a 90- to 120-decibel sound, equal to a lawnmower, car horn, or rock concert at close range, and the females click their wings in response. The concert, which is louder during hotter weather, only lasts three to four weeks; after this the adults reach the ends of their short lives aboveground and fall to the bases of the trees, where their bodies provide nutrients to the soil. The eggs hatch by late August, and the tiny nymphs fall to the ground and burrow under the soil, where the cycle begins again, during which time the nymphs of periodical cicadas will molt four times until finally the mysterious signal calls them back aboveground.

Since they can fly only a few hundred feet, cicadas tend to stay in the same grove of trees; as a result, all cicadas depend on the preservation of land, and are vulnerable to habitat loss, pesticide use, invasive species, and development. Open space preservation and responsible land management help ensure their survival, and will allow them to avoid extinction like Brood XI, gone since the mid-1900s. The ideal habitat for cicadas is land that will look the same 13 or 17 years later.

Keep an eye out in 2025 for the next nearby group of 17-year cicadas to emerge – Brood XIV in east-central PA and southern NJ. And Brood X will be back in 2038.